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Hot-tubbing in international arbitration: do we need a protocol?

Expert “hot-tubbing” (or witness conferencing), is the practice of expert witnesses providing evidence concurrently, so that they might engage in discussion and address questions in parallel (instead of being cross-examined individually by counsel).

“Hot-tubbing’” an Australian invention, has been adopted in civil litigation in England and Wales (and recent amendments to the Civil Procedure Rules (CPR), see Practice Direction (PD) 35, paragraph 11). The Technology and Construction Court (TCC) Guide even provides directions as to how hot-tubbing might be successfully conducted. Hot-tubbing has also proved increasingly popular in international arbitration. The International Chamber of Commerce (ICC) Commission Report on Controlling Time and Costs in Arbitration identifies witness conferencing as a technique that may be usefully adopted in suitable cases. The ICC report implicitly recognises that the practice has both advantages and disadvantages.


Theoretically, hot-tubbing makes the examination of experts efficient (and should reduce the amount of time taken up by examination). Advantages include:

  • Where experts are examined together, questions relating to a particular event or issue are only asked once, with each expert provided with an opportunity to present their views in relation to the event or issue in question.
  • Any disagreements between experts becomes immediately apparent and opposing expert witnesses (with whom the subject-matter of specific issues is very familiar) can challenge each other’s views (and this may also act as a restraint on expert excesses).
  • Exchanges between expert witnesses (and follow-up questions from the tribunal) may provide clarity, particularly in respect of complex technical issues. Expert conferencing may make the expert evidence more “user friendly” and give the tribunal a clearer picture of the issues.
  • Expert witnesses may feel more comfortable when examined in conference (as the pressure of being subject to direct questioning by counsel is removed) and this may result in clearer, more concise evidence.


The potential disadvantages are:

  • The parties (and their counsel) lose some control over the way their case is presented. Counsel do not have the same opportunity to present a story to the tribunal (or to catch the other side’s expert out in cross-examination) because they do not have control over the questions being put to the other side’s expert.
  • A great deal of reliance is placed on the arbitrators directing effective questioning of the experts and this requires that they have a comprehensive grasp of the (sometimes complex) issues in dispute.
  • The tribunal has to ensure that each party gets a fair opportunity to present its case (and to prevent the process becoming one-sided). The tribunal does not want to leave its award open to challenge on the basis of procedural irregularity.

Controlling the process

Hot-tubbing results in the abandonment of the traditional, counsel controlled, approach to expert examination familiar in international arbitration. Instead, the parties’ experts provide evidence together, in a questions and answers type session conducted by the tribunal (or counsel), in a process designed to create a confrontation of evidence which ultimately elicits the reality behind the issues in question. This means that hot-tubbing can be seen as a somewhat risky pursuit.

This perception is perhaps exacerbated by the absence of any detailed guidance as to the approach that should be taken to hot-tubbing in international arbitration. Whilst most institutional rules are sufficiently broadly drafted to allow hot-tubbing (and the International Bar Assocation (IBA) Rules on the Taking of Evidence in International Arbitration expressly provide for it (Article 8.3(f))), there’s no guidance as to the circumstances in which hot-tubbing can usefully be employed or as to how the process should be conducted. Instead, it is left to the parties, in conjunction with the arbitral tribunal, to decide how the process should proceed.

Hot-tubbing is therefore, in practice, often conducted on an informal basis (perhaps at the direction of the tribunal, during the same hearing in which the hot-tubbing takes place) and without a framework being put in place for its use. This disorganised and unstructured approach leads to the process becoming risky for the parties involved and less worthwhile (and defeats the purpose of the exercise, which is to create efficiency and clarity of evidence).

Where an unstructured, informal, approach is taken, the tribunal (or counsel) might not have had a chance to think about questions to direct to the experts (or worse still, may not have sufficient understanding to ask questions relating to the complex and technical issues on which the experts are opining). Further, without a defined list of issues or questions to be dealt with by the experts, questioning from the tribunal (or counsel) may become fragmented and jump from issue to issue (and counsel may interject, at will, with questions aimed at scoring points against the other side’s expert). Further still, unequal time and opportunity may be afforded to each expert (and one expert may take control of the process). Such a disorganised process only leads to confusion and inefficiency and should be avoided.

A protocol for hot-tubbing

To avoid any of hot-tubbing’s associated pitfalls and to realise its advantages (and, in turn, to reduce the risks highlighted above with regards to the abandonment of the counsel controlled approach to expert examination) a structured, organised and agreed approach is required.

The following checklist highlights some useful points to contemplate (or at least bear in mind) when considering hot-tubbing.

  • Decide whether opening statements are required. It might be helpful for the experts to present their views on key issues to the tribunal. If so, it should be established whether:
    • counsel can assist the experts in identifying the key issues to be highlighted to the tribunal;
    • exhibits (for example, PowerPoint presentations or handouts) should be used;
    • the experts should present their statements uninterrupted (by questions from the tribunal); and
    • a written opening statement should also be provided.
  • Draw up an agenda or a list of issues to be dealt with by expert conferencing and ensure that sufficient time is allocated to each item/issue.
  • Consider procedural issues such as whether:
    • cross-examination of each expert is permitted in respect of particular issues during expert conferencing or, alternatively, whether cross-examination should only take place after expert conferencing has been concluded (and in each of the above instances whether a “chess clock” method of time allocation is used);
    • the tribunal (or counsel) should initiate the expert conferencing (and associated discussions);
    • the tribunal should ask questions relating to each expert’s credibility (or whether this should be left to counsel);
    • the experts decide between themselves who is best able to answer particular questions (or whether questions should be directed at a particular expert);
    • whether one expert can question the other (in the event that an expert takes on the role of cross-examining the other expert);
    • whether the experts will be permitted to adduce fresh evidence during expert conferencing;
    • whether weight is given to written testimony not addressed in expert conferencing; and
    • how the expert conferencing should conclude and whether there is a need for closing statements at the conclusion of expert conferencing.
  • Consider practical issues such as:
    • whether a translator is required (if experts speak different languages);
    • seating arrangements (a semi-circular “audience” with the tribunal in the centre may reduce the scope for inappropriate cross-examination); and
    • arrangements for experts to view and discuss key documents, diagrams, and pictures.

In suitable cases, hot-tubbing is a very useful technique but in order to deploy it in appropriate cases, and to best effect, a formal protocol is needed.

Bryan Cave Leighton Paisner Alasdair McAlpine

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